Advanced batteries based on sodium metal halide chemistry (“sodium metal halide cells”) have been explored for use in electric vehicles, uninterruptable power systems (UPS), and telecom backup systems because of their high specific energy, power density, long cyclic life, and sustained high-power discharge over frequent cycling as compared to conventional lead-acid cells. One issue with sodium metal halide cells is that the distribution of liquid electrolyte throughout the cell cathode granule bed can become non-uniform after frequent cycling. In particular, following many charge-discharge cycles, the cathode granule cathode bed particle morphology may change and/or degrade, developing heterogeneities such as regions of pore occlusion and channeling, thereby resulting in portions of the granule bed which are inaccessible to liquid electrolyte, and reducing the sodium cell charge capacity. Furthermore, this granule bed degradation can worsen with successive cell cycling, significantly decreasing cell lifetime.
Wright (U.S. Pat. No. 5,143,802) discloses embedding a porous conductive carbon felt slab structure in the granule bed along the length of the cathode compartment in order to maintain more uniform distribution of liquid electrolyte throughout the granule bed.
The inventors have recognized a problem with the above solution. Namely, a carbon felt slab structure is a monolithic structure that divides and isolates portions of the granule bed on either side of the carbon felt slab structure. As such, the carbon felt slab structure reduces cross-communication (e.g., including transport of ions, electrons, and liquid electrolyte) between the isolated portions of the granule bed, thereby reducing charging and discharging efficiency during cell operation. Furthermore, during manufacture of a sodium metal halide cell, the carbon felt slab structure may hinder uniform filling and distribution of the granule bed in the cathode compartment which can generate a load imbalance in the cell and further reduce cell operating efficiency.